jmarsh wrote:"Could" be possible, but the reality is it simply never happened.
It didn't? Did you research this?
jmarsh wrote:Configuration register bits that are undefined are routinely declared as "must be zero" and trying to set them often causes a fault, precisely to safeguard forward compatibility.
Did you research whether or not it does in this specific case?
Because I can think of various examples where undefined bits can be set to 1 without causing a fault. In fact, that is how Intel recommends to detect CPUs that predate the CPUID instruction.
jmarsh wrote:Hardly a scenario worth caring about;
Is it? Did you research it?
My experience with Win95 software is that quite a lot of it didn't work at all on any NT-based Windows, and sometimes not even on later Win9x versions, because of all the low-level hacks that were used.
You have to understand that especially with games, people came from a culture of DOS, home computers and consoles, where you would own the entire system, and (ab)use the hardware to your heart's delight, to extract the maximum performance out of it.
I said FPU/MMX state - neither are usable unless co-processor emulation is turned off.
What's your point?